How to check CPU clock speed in Linux

Checking CPU clock speed in Linux clarifies whether a system is running at the expected base frequency, reaching boost clocks under load, and scaling down correctly when idle. Accurate clock information helps diagnose thermal throttling, power-saving issues, and performance inconsistencies across workloads.

Under Linux, tools such as lscpu, dmidecode, and runtime monitors read data from firmware tables, /proc/cpuinfo, and kernel cpufreq interfaces. These sources expose minimum and maximum frequencies as well as per-core values, making it possible to compare vendor specifications with what the system actually reports.

Boost behavior, virtualization layers, and power-management profiles can cause reported clock speeds to fluctuate or differ slightly from marketing numbers. Sampling multiple tools and observing values under load provides a more realistic view of how a CPU behaves in practice.

1. Open a terminal with access to sudo.

   $ whoami
   user

2. Display summarized CPU information, including the model name and advertised frequency.

   $ lscpu | grep ^Model\ name
   Model name:                      Intel(R) Core(TM) i7-10510U CPU @ 1.80GHz

   Related: How to check CPU information in Linux

3. List the minimum and maximum frequencies reported by lscpu in MHz.

   $ lscpu | grep -E 'CPU MHz|CPU max MHz|CPU min MHz'
   CPU MHz:                         1683.0000
   CPU max MHz:                     4900.0000
   CPU min MHz:                      400.0000

   CPU max MHz and CPU min MHz reflect kernel scaling limits for the current governor.

4. Read firmware-reported maximum speed using dmidecode.

   $ sudo dmidecode -t processor | grep "Max Speed"
     Max Speed: 4900 MHz

   dmidecode parses system firmware tables and may expose hardware identifiers; output should be handled carefully on shared systems.

5. Inspect firmware-reported current speed from the same source.

   $ sudo dmidecode -t processor | grep "Current Speed"
     Current Speed: 1683 MHz

6. Check live per-core frequencies from /proc/cpuinfo for a more granular view.

   $ grep "cpu MHz" /proc/cpuinfo
   cpu MHz         : 900.000
   cpu MHz         : 2300.000
   cpu MHz         : 2477.000
   cpu MHz         : 2300.000
   cpu MHz         : 2300.000
   cpu MHz         : 902.000
   cpu MHz         : 2300.000
   cpu MHz         : 900.000

   Running watch -n 1 'grep "cpu MHz" /proc/cpuinfo' shows how frequencies change over time.

7. Install a real-time monitoring tool such as auto-cpufreq on Ubuntu to visualize scaling behavior.

   $ sudo snap install auto-cpufreq

   Installing additional monitoring tools increases system load slightly; monitoring during benchmarks can influence measured frequencies and performance.

8. Start live monitoring with auto-cpufreq to see minimum, maximum, and current frequencies for all cores.

   $ sudo auto-cpufreq --monitor
   ##### snipped
   ------------------------------ Current CPU stats ------------------------------
   
   CPU max frequency: 4900 MHz
   CPU min frequency: 400 MHz
   
   Core  Usage Temperature Frequency
   CPU0:   0.0%     44 °C      900 MHz
   CPU1:   3.0%     43 °C     2300 MHz
   CPU2:   5.9%     43 °C     2477 MHz
   CPU3:   1.0%     42 °C     2300 MHz
   CPU4:   0.0%     44 °C     2300 MHz
   CPU5:   2.0%     43 °C      902 MHz
   CPU6:   1.0%     43 °C     2300 MHz
   CPU7:   0.0%     42 °C      900 MHz
   ##### snipped

   Values shown by auto-cpufreq derive from kernel frequency scaling interfaces and reflect real-time behavior under current load and thermal limits.

9. Compare the maximum and current frequencies reported by lscpu, dmidecode, /proc/cpuinfo, and auto-cpufreq to verify that base and boost speeds align with vendor specifications and observed runtime values.

   Large discrepancies between firmware, kernel, and live readings can indicate misconfigured power profiles, outdated firmware, or thermal throttling that limits sustained performance.